THE avian flu virus that infected eight members of the same family in Indonesia last month — killing seven of them — underwent a small mutation as it swept through the family, the World Health Organisation has concluded.

But the mutation was not sufficient to turn the H5N1 virus into an easily-transmissible human form, the change that has been dreaded ever since the lethal form of H5N1 first appeared.

The conclusion emerged at the end of a three-day consultation in Jakarta that brought together experts from around the world to assess the situation in Indonesia, where avian flu has already killed 39 people.

The cluster of cases, the largest yet recorded, involved a family living in the village of Kubu Sembelang, in North Sumatra. The family lived in close proximity to one another, and the infection caught from birds by one family member spread to the others.

Keiji Fukuda, coordinator of the WHO’s global influenza programme, said that a woman who fell ill had remained in the same room as several family members. "So when she was coughing, they were very close to her, so there was close contact in a small room over many hours.

"We describe it as limited non-sustained transmission person-to-person," he said.

Virological analysis of samples showed that those from a 10 year-old boy were slightly different from the others. Such genetic shifts take place all the time with flu viruses.

Tim Uyeki, an epidemiologist from the US Centres for Disease Control and Prevention, said that the changes were small and that the H5N1 virus did not pass outside the cluster and died with the father.

"It stopped. It was dead end at that point," he said, stressing that there was no reason to raise alarm bells. More than a month has passed - more than twice the incubation period - since the father of the family was the last to die, with no new cases.

Aburizal Bakrie, Indonesia’s Welfare Minister, reinforced the message. "There is no sustained human-to-human transmission," he said.

However, the cluster is just the situation in which such a change could occur, and prompted the Indonesian Government to call the expert consultation. H5N1 avian virus is firmly entrenched in poultry flocks throughout much of the country, and continues to cause human cases among those in close contact with birds.

The more often clusters of this sort arise, the more probable becomes the transition of H5N1 avian flu into a pandemic human strain. The basic issue is the need to control avian flu, so that families like the ill-fated people in Kubu Sembelang cannot act as test-tubes in which the flu virus goes through its quick-change routines to emerge as a deadly pandemic strain.

Bird flu has killed at least 130 people worldwide since it appeared in Asian poultry stocks in late 2003.

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